U.S. patent number 4,164,690 [Application Number 05/790,928] was granted by the patent office on 1979-08-14 for compact miniature fan.
Invention is credited to Rolf Muller, Gunter Wrobel.
United States Patent |
4,164,690 |
Muller , et al. |
August 14, 1979 |
Compact miniature fan
Abstract
A compact miniature fan has an air-guidance housing of
rectangular parallelepiped configuration. The housing has two
opposite end walls and side walls. One end wall is provided with an
air inflow opening. One side wall is provided with an air outflow
opening. The other end wall comprises a base plate. Mounted within
the housing is an electric motor of flat overall shape. The stator
and rotor of the motor define a planar air gap. The stator includes
a magnetically conductive flux-return structure mounted on the base
plate and a stator winding comprised of a plurality of flat coils
mounted on the flux-return structure. The rotation axis of the
rotor extends in the direction from one to the other of the end
walls of the air-guidance housing. A radial fan wheel is provided
within the housing, mounted on and coaxial with the rotor of the
motor.
Inventors: |
Muller; Rolf (St. Georgen,
Schwarzw., DE), Wrobel; Gunter (Villingen,
DE) |
Family
ID: |
4291177 |
Appl.
No.: |
05/790,928 |
Filed: |
April 26, 1977 |
Foreign Application Priority Data
|
|
|
|
|
Apr 27, 1976 [CH] |
|
|
005294/76 |
|
Current U.S.
Class: |
318/400.41;
310/63; 417/410.1; 417/423.7; D23/371 |
Current CPC
Class: |
F04D
25/0653 (20130101); H02K 29/08 (20130101); H02K
7/14 (20130101) |
Current International
Class: |
F04D
25/06 (20060101); F04D 25/02 (20060101); H02K
29/08 (20060101); H02K 7/14 (20060101); H02K
29/06 (20060101); H02K 029/00 () |
Field of
Search: |
;318/138,254
;310/62,63,68,268 ;417/410 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Rubinson; Gene Z.
Attorney, Agent or Firm: Striker; Michael J.
Claims
We claim:
1. A compact miniature fan, comprising an air-guidance housing of
rectangular parallelepiped configuration having two opposite end
walls and side walls, one of the end walls being provided with an
air inflow-opening, one of the side walls being provided with an
air outflow opening, the other of the end walls being comprised of
a base plate; an electric motor of flat overall shape mounted
within the housing, the motor comprising a rotor and a stator
together defining a planar air gap, the stator including a
magnetically conductive flux-return structure mounted on the base
plate and a stator winding comprised of a plurality of flat coils
mounted on the flux-return structure, the rotation axis of the
rotor extending in the direction from one to the other of the end
walls of the housing; and a radial fan wheel within the housing
mounted on and coaxial with the rotor of the motor.
2. The fan defined in claim 1, said other end wall of the housing
being a closed end wall and consisting of the base plate.
3. The fan defined in claim 1, the base plate being generally
rectangular, the flat coils comprising two flat coils located on
one diagonal of the base plate.
4. The fan defined in claim 3, the motor being a four-pole motor,
the flat coils in plan view having the elongated and approximately
elliptical shape of a racetrack, the longitudinal axis of each flat
coil extending generally perpendicular to said diagonal.
5. The fan defined in claim 4, the magnetically active sections of
the coils being spaced from one another by about 130 electrical
degrees.
6. The fan defined in claim 1, the magnetic flux-return structure
comprising a plurality of concentric and coplanar annular plates
made of soft ferromagnetic material.
7. The fan defined in claim 6, the concentric annular plates being
insulated from each other.
8. The fan defined in claim 1, the magnetic flux-return structure
of the stator being at least partly embedded within the material of
the base plate, whereby to reinforce the base plate.
9. The fan defined in claim 2, the stator furthermore including a
bearing pipe mounted on the base plate, the rotor including a rotor
shaft journalled on the bearing pipe, the rotor furthermore
comprising a hat-shaped structure including a central crown-shaped
part mounted on the rotor shaft and a surrounding radially
outwardly extending annular brim-shaped part, the annular
brim-shaped part carrying the generally radial fan blades of the
radial fan wheel.
10. The fan defined in claim 9, the hat-shaped structure being a
deep-drawn sheet-steel element, the crown-shaped part surrounding
the bearing pipe and extending into the brim-shaped part in the
direction from said one to said other end wall of the housing, the
fan blades being provided on the side of the brim-shaped part which
faces said one end wall of the housing, the rotor furthermore
including a permanent-magnet rotor-magnet structure mounted on the
side of the brim-shaped part which faces the base plate.
11. The fan defined in claim 1, the fan wheel being a one-piece
molded element mounted on the side of the rotor facing away from
the base plate.
12. The fan defined in claim 1, the rotor being a permanent-magnet
rotor.
13. The fan defined in claim 1, the motor being a collectorless
D.C. motor and including a magnetic-field-responsive transducer
operative for generating a signal indicative of the angular
position of the rotor, and control circuit means operative in
dependence upon said signal for controlling the energization of the
coils of the stator winding.
14. The fan defined in claim 13, the rotor-position transducer
comprising a Hall generator.
15. The fan defined in claim 13, the rotor being a permanent-magnet
rotor, the rotor-position transducer being arranged in the
stray-flux region of the rotor.
16. The fan defined in claim 13, the rotor-position transducer
including an element having a field-sensitive surface, this element
being so arranged that the field-sensitive surface is located
alongside and flush with the face of one of the flat coils of the
stator at the planar air gap of the motor.
17. The fan defined in claim 15, the permanent-magnet rotor
comprising an annular axially polarized permanent magnet, the
axially polarized pole sectors of the annular magnet being
separated by intermediate pole-gap sectors, the annular permanent
magnet at each of its pole-gap sectors having a reduced-diameter
setback.
18. The fan defined in claim 17, the reduced-diameter setbacks
being flat setbacks, each setback having an angular span
corresponding to between about 50 and 100 electrical degrees.
19. The fan defined in claim 17, the axially polarized permanent
magnet of the rotor being a stamped member made of a mixture of
hard ferrites and rubber or synthetic plastic.
20. The fan defined in claim 17, the setbacks being flat peripheral
setbacks.
21. The fan defined in claim 15, the permanent-magnet rotor
comprising an annular axially polarized permanent magnet, the
axially polarized pole sectors of the annular magnet being
separated by intermediate pole-gap sectors, each pole-gap sector
being inclined relative to the radial direction, the inclination
being such that as one proceeds along the length of each pole-gap
sector from the radially innermost to the radially outermost part
thereof the pole-gap sector extends in the direction opposite to
the rotation direction of the rotor, the rotor-position transducer
being located just ahead of one of the flat coils of the stator
when considered in the direction of rotor rotation.
22. The fan defined in claim 13, the rotor being a permanent-magnet
rotor comprising an annular axially polarized permanent magnet, the
axially polarized pole sectors of the annular magnet being
separated by intermediate pole-gap sectors, the circumferential
distribution of the magnetization of the annular magnet being
generally trapezoidal, and the angular span of the pole-gap sectors
being small compared to that of the pole sectors.
23. The fan defined in claim 22, the stator furthermore including
at the inner side of the annular rotor magnet a soft ferromagnetic
element located and configured to produce a cooperation with the
rotor magnet a reluctance torque when the rotor is in the angular
positions thereof corresponding to gaps in the electromagnetic
torque of the motor.
24. The fan defined in claim 1, the stator furthermore including a
bearing pipe mounted on the base plate, the rotor being a
permanent-magnet rotor and including a rotor shaft, further
including two axially spaced ball bearings journalling the rotor
shaft on the bearing pipe, the motor including means for axially
stressing at least one of the two ball bearings to reduce rotor
play in the axial direction.
25. The fan defined in claim 24, the means for axially stressing at
least one of the two ball bearings being comprised by portions of
the rotor extending between the permanent-magnet structure thereof
and the rotor shaft and operative for transmitting axial stressing
force to at least one ball bearing by deriving that force from the
axial force of attraction between the permanent-magnet structure of
the rotor and the flux-return structure of the stator.
26. The fan defined in claim 24, the means for axially stressing at
least one of the ball bearings comprising biasing spring means
axially braced against such ball bearing.
27. The fan defined in claim 26, the bearing pipe being provided
with a radially inwardly extending stop, the one of the ball
bearings which is axially stressed being provided with an annular
bearing member, the biasing spring means comprising a stationary
biasing spring confined between and braced against the stop and the
annular bearing member.
28. The fan defined in claim 1, the volume occupied by the housing
of the fan being smaller than 400 cm.sup.3.
29. The fan defined in claim 28, the volume occupied by the housing
of the fan being smaller than 200 cm.sup.3.
30. The fan defined in claim 13, the collectorless D.C. motor
having a rated speed higher than 3500 rpm.
31. The fan defined in claim 30, the power consumption of the motor
being at most 3 watts.
32. The fan defined in claim 13, the air-guidance housing
furthermore including a generally spiral-shaped air-guide wall
between the end walls of the housing, the spiral-shaped air-guide
wall being radially spaced from the radial fan wheel by a distance
which decreases proceeding in the direction of rotation of the fan
wheel, the spiral-shaped air-guide wall together with at least one
of the side walls defining at least one internal compartment, said
control circuit means of said collectorless D.C. motor including
electronic components housed within said internal compartment.
33. The fan defined in claim 1, the magnetically conductive
flux-return structure having recesses distributed about the
rotation axis of the rotor, the recesses being so configured and
angularly located as to produce in cooperation with the rotor of
the motor a reluctance torque when the rotor is in the angular
positions thereof corresponding to the gaps in the electrogmagnetic
torque of the motor.
34. The fan defined in claim 28, the overall dimension of the
housing measured in the direction of a diameter of the rotor being
approximately three times as great as the overall dimension of the
housing measured in the direction of the rotor rotation axis.
35. The fan defined in claim 28, the housing being approximately a
cube.
36. The fan defined in claim 28, the overall dimension of the
housing measured in the direction of a diameter of the rotor being
between about one and three times as great as the overall dimension
of the housing measured in the direction of the rotor rotation
axis.
37. The fan defined in claim 1, the fan wheel being mounted on the
side of the rotor facing away from the base plate, the fan wheel
not encircling the magnetic circuit structure of the motor but
instead being axially adjacent the magnetic circuit structure of
the motor.
Description
The invention relates to a compact miniature fan with a radial fan
wheel driven by a coaxial electromotor, the fan wheel being
enclosed by an air-guidance housing of rectangular parallelepiped
configuration, in one of whose end faces the air enters and out of
at least one of whose side faces the air discharges.
It relates in particular to such a fan of high rotary speed, with
high rotary speed being understood to be above 3500 rpm. Fans of
smaller structural dimensions are today used above all in
electronic devices in large numbers for cooling of the electronic
components. As a result of progress in electronics, these devices
are often made very small; it has been found that, with fans
provided with conventional means, minaturization without resort to
special expedients is not possible beyond a certain extent. This is
troublesome in many applications, e.g., in aircraft electronics,
where components are very tightly packed together, or with portable
devices, e.g., measuring devices, radio devices, or the like. With
the last-mentioned devices, there is the additional factor, that
the power requirement of the fan (which may be driven inter alia
from batteries) should be as small as possible; that is, for such
applications, conventional fans with their poor efficiency (10 to
15%) usually cannot be employed. Where efficiency was not the main
consideration, the use of known fans of the general type in
question involved energization at medium frequency (400 Hz).
An object of the invention is accordingly to be seen in the
creation of a compact fan having good air throughput and avoiding
the disadvantages in question.
According to the invention this is achieved by the expedients
specified in claim 1. With such a construction, the magnetic
flux-return structure of the motor simultaneously serves as a
reinforcement for the motor housing, that is, it is employed in the
fan construction as a load-bearing component. The flat motor of
disk-like configuration despite its small dimensions produces a
good torque, relatively fast starting, and makes possible a
relatively large air inflow cross section and a simple arrangement
of the blades of the radial fan within the fan housing,
particularly in the case of extremely flat and compact fans. Also,
its production is economical.
These flat motors, which are maintenance-free and produce less
radio interference, are known as collectorless D.C. motors. The
latter have, particularly when they are constructed in accordance
with the teaching of U.S. Pat. No. 3,840,761, a very considerable
efficiency even at low power, e.g., up to 60% with a 3-watt motor,
and they make possible a considerably high air throughput even with
small fan sizes, due to the high rotary speed of which they are
capable. Because this rotary speed is limited in the upward
direction practically exclusively by fan noise, one can, e.g., in
aircraft where noise generation plays a small or no role, operate
at very high rotary speeds. A further advantage of D.C. motors is
that they are optimally matchable to the operating voltages of
electronic devices and, e.g., with a voltage of 12 volts
particularly good efficiency can be achieved. Also, their rotary
speed and accordingly their air throughput is variable within wide
limits in a very simple way by varying their operating voltage, so
that with a single fan size the needs of various practical
applications can be satisfied, i.e., stocking by manufacturers and
customers can be very markedly reduced.
Furthermore, battery operation is possible and excellent, e.g., in
climate-control systems in buses and cruise tractors, without
having to worry about a quick exhaustion of the battery when the
vehicle is at a standstill.
Further details and advantageous modifications of the invention are
to be found in the illustrative embodiment described below and
illustrated in the drawing, but to be understood not to limit in
any way the scope of the invention, as well as in the dependent
claims.
The drawing shows:
FIG. 1 a first perspective illustration of a radial fan in
accordance with the invention on an enlarged scale, with
dimensional units being indicated in width and height directions to
make clear the dimensions.
FIG. 2 a second somewhat different perspective illustration of the
radial fan of FIG. 1 with a mounting modification indicated in
broken lines.
FIG. 3 a section through the radial fan of FIGS. 1 and 2, seen
along the line III--III of FIG. 4.
FIG. 4 a partly broken-away top view of the radial fan of FIGS. 1
to 3.
FIG. 5 a section, seen along the line V--V of FIG. 3, with some
details of the shaft mounting not being illustrated.
FIG. 6 a circuit for powering the radial fan of FIGS. 1 to 5.
FIG. 7 graphs for explaining the manner of operation.
FIGS. 1 to 4 clearly show on an enlarged scale the construction of
the radial fan 10. The latter has a base plate 11 designed as a
molded item made of synthetic plastic, e.g., fiberglass-reinforced
plastic (GFK), upon which there is mounted by means of three screws
12 an upper housing part 13 which preferably is likewise made of
GFK; the part 13 has at its upper side a circular air inflow
opening 14 and at a forward side wall 15 a rectangular air outflow
opening 16 which, for example in the exemplary embodiment and as
shown in FIG. 1 for the sake explanation, has the dimensions
17.times.38. In its entirety, the illustrated radial fan 10 is only
about 23 mm high and its base outline is 73.times.73 mm; i.e., it
is extremely flat and compact and has a volume of less than 125
cm.sup.3. As particularly clearly shown in FIG. 3, the upper
housing part 13 is mounted air-tight on the base plate 11, and the
base plate, as shown in FIG. 4, has external recesses 20 for
accepting the side walls of the upper part 13 and an internal
spiral-shaped recess 21 for accepting a spiral-shaped air guide
wall 22 provided on the upper part 13; air guide wall 22 rightward
at 18 merges into the backmost section of the right exterior wall
19.
Serving to mount the radial fan 10 are holes 17 on two
diametrically opposite corners of the base plate 11, the external
wall of the upper part being at these locations set back, as
illustrated.
FIG. 2 indicates in broken lines an alternative intended for
universal mountability. The tab-shaped extensions 114 of the base
plate 11 project beyond the housing part 13 and have mounting holes
17 which lie on the diagonal 133 perpendicular to the straight line
33 in FIG. 4. The cover wall 111 of the upper housing part 13 is
shown in FIG. 2 (in broken lines) to likewise have such tab-shaped
extensions 115 with mounting holes 117 on the same diagonal 133. By
means of the extensions 115, the flanges of the compact fan can be
directly mounted on, for example, a housing wall out of which the
fan is to suck air.
In the hollow spaces 23, 24 between the recesses 20 and 21 the
electronic circuit elements of the motor are arranged, if the motor
in accordance with a preferred concept of the invention is designed
as a collectorless D.C. motor. A connector cable 124 leads out from
the hollow space 23.
The Hall generator 146 shown in FIG. 4 in broken lines and provided
as an alternative to 46 lies with its sensitive surface alongside,
parallel and with the coil 28 flush at the air gap in the edge
region 45, 47 of the magnet 30. This modification, relative to the
previous vertical position of the Hall generator 46, permits
incorporation of the Hall generator 146 into a printed circuit
lying in the same plane, which latter is indicated by the
broken-line indication of its electronic elements; this is
advantageous in terms of production. These electronic elements are
the principal heat-generating components, and as a result
furthermore lie in the region of the air flow.
The fan 10 derives its flat form from the construction of the motor
driving it, here designed as a flat motor 25. The magnetic
flux-return structure of motor 25 is in the form of concentric
rings 26 of soft iron; advantageously, these are insulated from one
another and are secured in the base plate 11 in the illustrated
manner in a recess, e.g., directly during injection (molding) of
the base plate 11. If the base plate 11 is produced in an automatic
injection cycle, the rings 26 can be incorporated in the injected
base plate by means of cement or ultrasonic means more economically
with respect to production, than if they were injection-molded in.
The rings 26 are, e.g., each about 1 mm thick and are located one
within the other in the manner of old-fashioned cooking ranges. Of
course, other subdivisions of the magnetic flux-return structure
are possible, e.g., by means of radial slits.
Particularly advantageous, especially for high rotary speeds, are
straight-line or slightly curved indentations which extend at an
angle of 20.degree. to 70.degree., e.g., 30.degree., to the tangent
at the outer periphery of the flux-return ring in direction away
from the respective point of contact of this tangent, so as to have
at least the length of the pole spacing (in circumferential
direction) and to be at least so densely distributed upon the
periphery that each conceivable radial section crosses at least one
to two of such indentations. A radial subdivision of the
flux-return ring is then unnecessary. The rigidity of a thusly
configured flux-return ring is possibly lower, but its
effectiveness in suppressing eddy currents is increased. This can
be further increased, if the flux-return ring provided with
indentations whose cut surfaces still project out of the plate
plane, receives by bonding for example an insulating phosphate
coating, and then the ring prior to injection in the fan housing is
turned flat. By means of this expedient, eddy currents are markedly
damped.
An insulating coating is advantageous on the first-mentioned
radially subdivided more rigid flux-return rings 26, which serve as
a reinforcement for the plate 11 and stiffen the latter
particularly well.
The two coils 27 and 28 of the stator are secured directly above
the rings 26, e.g., by cementing. These coils can, for example,
likewise each have a height of 1 mm, in order to produce a small,
magnetically effective air gap 29 of for example about 2 mm between
the rotor magnet 30 and the flux-return rings 26. The flux-return
rings 26 and the rotor magnet 30, which is designed as an axially
polarized 4-pole ring magnet, have about the same basic outline and
mutually cover each other over, as clearly shown in FIG. 3.
The coils 27 and 28 have, as illustrated, their middle points each
located on a straight line 33 parallel to the longer of the two
housing diagonals. In plan view, they have approximately the shape
of a sports arena, and their longitudinal axes are each oriented
perpendicular the straight line 33. Their magnetically active
sections in the illustrated embodiment are spaced from each other
by about 140 electrical degrees. They are both two-wire wound and
connected to each other with the same sense. From connection A
(FIG. 5) of the coil 28, there thus leads a wire through the latter
and through the coil 27 to the connection E located there, and the
same applies for the connections A' and E'. If, for example, a D.C.
voltage is applied between A and E, then both coils generate
equally strong magnetic fields with the same direction, e.g., in
both cases a north pole on top. The situation is analogous upon
application of a D.C. voltage between A' and E'.
An approximately quadratic soft iron piece 38 is fixedly cemented
on a central projection 35 of the base plate 11 in which a bearing
pipe 36 for receiving the rotor shaft 37 is secured; the short iron
piece 38 is located above the two coils and is located axially and
radially inward of the magnet ring 30; the soft iron piece 38 is
known per se from U.S. application Ser. No. 706,550 and reference
is expressly made thereto to avoid unnecessary length; the diagonal
of soft iron piece 38 includes an angle .epsilon. with the diagonal
33.
The soft iron piece 38 cooperates with the stray flux at the inner
periphery 40, in order to generate during motor operation a
reluctance torque whose driving components are effective in the
gaps of the electromagnetic drive torque, such as is the subject
matter, inter alia, of U.S. Pat. No. 3,840,761. The rotational
direction of the flat motor 25 is denoted by 43. For a simplified
and economical design, the stationary flux-return structure 26 is
so designed that it in cooperation with the rotor magnet 30
produces the desired reluctance torque, e.g., by means of V-shaped
cut-outs on the outer periphery of the stationary flux-return iron
at the spacing of the pole spacing, and the soft feeromagnetic
molded piece 38 can then be eliminated. The flux-return ring can
then be designed in corresponding shape as a cheap stamped
component.
With this design, however, the useful torque may be reduced, since
the flux-return cross section is diminished.
The magnet ring 30 has a trapezoidal magnetization as schematically
denoted in FIG. 7A by Bnutz. Its pole gaps 44--these are not
visible upon the ring 30, and are instead merely gaps in its
magnetization--are curved from inward toward outward opposite to
the rotation direction, which is likewise the subject matter of
U.S. Pat. No. 3,840,761, to the contents of which reference is
expressly made, in order to avoid lengthiness.
Around the outer ends of the pole gaps 44, the outer periphery 45
of the magnet ring 30 has four clearances in the form of
flattened-off portions 47, each occupying an angular range of
approximately 50 to 100 electrical degrees, in the exemplary
embodiment about 80 electrical degrees; their function cannot be
permitted to be interchanged with that of the aforementioned
V-shaped cut-outs for the generation of the auxiliary reluctance
torque. Arranged on the base plate 11 opposite to these
flattened-off portions is a galvanometric sensor 46, which in the
exemplary embodiment is located in the stray flux of the rotor
magnet and is designed as a Hall-IC, e.g., of the type Honeywell 63
SS 2 C.
This Hall-IC is controlled by the stray flux B.sub.Streu (FIG. 7A)
at the outer periphery 45, and due to the flattened-off portions 47
of which one is also visible in FIG. 1, this stray flux has
relatively large gaps Q which are substantially wider than the
narrow pole gaps P of the useful flux in the air gap 29. By means
of this simple expedient, if the magnet ring 30 is made for example
from a mixture of hard ferrites and rubber or the like, i.e., a
so-called rubber magnet, then one can simply stamp it out in its
entirety in its final form--here however for the generation of a
desired shape for the Hall voltage--and in the case of the
magnetization practically no more concern about the form of this
output voltage u.sub.H of the Hall-IC 46 need be taken, since
u.sub.H (this voltage is practically proportional to B.sub.Streu)
can be modified in a very simple way by alteration of the
flattened-off portions 47.
The shaft 37 is journalled in the bearing pipe 36 by means of two
ball bearings 50 (upper) and 51 (lower). 50 bears with its outer
ring against a circlip 52 which is secured in the bearing pipe 36.
The inner ring of 51 bears against a circlip 53 on the shaft 37, as
a result of which the spring 54 supported upon the circlip 52
presses a ring 55 against the outer ring of 51 and the latter is
therefore axially braced against the inner ring. Due to the
magnetic axial pull in the air gap, the inner and outer ring of the
ball bearing 50, too, are axially braced to each other, so that
both bearings turn without play, which is very important for
quietness of operation and service life at high rotary speeds.
At the upper end of 37 there is secured a bushing 57, and on the
latter there is secured a deep-drawn hat-shaped molded piece 58
which surrounds the bearing pipe 36 at a small spacing and on whose
flat part 59, corresponding to the brim of the hat, at the
underside thereof, the ring magnet 30 is fixedly cemented, and at
the upper side of part 59, a molded part 60 is secured, e.g., by
rivets; at the periphery of the molded part 60 there are provided
sixteen radial fan blades 63, whose shape can be clearly seen from
FIGS. 1 and 2.
Because the section of the molded part 58 corresponding to the
upper part of the hat closely surrounds the bearing pipe 36, one
obtains a large air inflow cross section and simultaneously an
excellent, very stable mounting of the fan wheel 60, so that air
(arrow 64 in FIG. 3) can readily flow into the fan, with little air
resistance produced at the inflow side. Furthermore, despite the
small overall height of the radial fan 10, there is nevertheless
available for the blades 63 a considerable structural height; and
naturally one could by increasing the height of the fan markedly
increase this blade height without resort to special expedients,
from which it is clear that the space utilization, if one
lengthened the blades for example to twice the thickness of the
housing parallelepiped, would increase drastically, and such a fan
in conjunction with the large inflow cross section produced by the
invention can be configured very advantageously with respect to
flow.
The invention is additionally advantageous for cube-shaped and
similar compact miniature fans, of course assuming that radial fan
wheels are employed, since they assure a small ratio d/e and, if
one increases the axial blade dimension a up to a cube-shaped
configuration for the fan, the ratio a/h becomes greater (and
better). The combination of minimal d/e and maximal a/h is optimal
for the volume within the fan housing utilized for flow (a, d, e,
h; see FIG. 3). h is the axial dimension, g the dimension of the
housing corresponding to the diameter of the fan wheel; a is the
effective axial blade length.
Even the air outlfow cross section, i.e., the opening 16 in FIGS. 1
and 2, is remarkably large, a/h, i.e., despite the small dimensions
of the fan wheel 10 (as illustrated) one achieves in its useful
rotary speed range (about 3000 to 7000 rpm) a very good air
throughput with low power consumption (about 3 watts at 4500
rpm).
In order to better explain the purpose to be achieved by the
flattened-off portions 47, FIG. 6 depicts a circuit for controlling
the current in the motor windings. These are denoted in FIG. 6 by
A, A' and E, E', just as in FIG. 5. Of course, the circuits of U.S.
application Ser. No. 570,837 could also be used, with the
blocking-protected circuits of both Offenlegungsschriften also
deserving mention in particular, since these blocking-protected
circuits are particularly advantageous in the case of fans.
According to FIG. 6, one current terminal of the Hall-IC 46 is
connected via a resistor 65 with a negative line 66, the other
directly with a positive line 67. Its left output leads directly to
the base of a pnp transistor and--via a resistor 69--to the emitter
of a pnp transistor 70. The right output of 46 leads to the base of
70 and--via a resistor 73--to the emitter of 68. 69 and 73 are
negative-feedback resistors of for example 1000 ohms each, and they
serve to make the motor currents almost into an image of the
variation of u.sub.H above or below a threshold value denoted in
FIG. 7A by +u.sub.s or -u.sub.s, respectively. The collector of 68
leads to the base of an npn power transistor 74, the collector of
40 to the base of an npn power transistor 75. Between the
collectors of 74 and 75 and the positive line 67 are connected the
two motor windings 76 and 77, whose winding-senses are indicated by
the capital letters.
During operation of the IC 46, if a pole gap 44 or the region
surrounding it is located opposite to a flattened-off portion 47,
its left and right outputs have approximately the same potential,
and 68 and 70 are both non-conductive, likewise 74 and 75. When
then the end of a flattened-off portion 46 approaches, so that for
example its left output becomes more negative and its right output
more positive, it will still be the case that neither of the
transistors 68 or 70 will conduct, since the threshold voltage
u.sub.s of transistor 68 has still not been reached. Only when
u.sub.H becomes larger than u.sub.s will transistors 68 and 74
conduct, the winding 76 receive current, and the current i.sub.76
in the manner shown in FIG. 7B increases monotonically, i.e.,
without jumps. When the next flattened-off portion 47 is reached,
one will again fall below u.sub.s and i.sub.76 becomes zero. Next,
then--in FIG. 6 the circuit is completely symmetrical--in a
completely analogous manner the winding 77 is switched on. The
motor currents i.sub.76 and i.sub.77 are thus switched on and off
gradually, and one achieves in the desired way a large current gap
Q, which inter alia contributes very much to quiet operation of the
motor, increases efficiency, and loads the transistors 74 and 75
minimally, since both the switch-on and the switch-off of the motor
current coincides with a high counter-emf in the windings.
All the components of the circuit of FIG. 6 can be conveniently
provided in the hollow spaces 23 and 24 of the housing. The
solution with the Hall-IC in the stray field is thus a preferred
solution precisely for very small radial fans; it signifies,
however, a certain expense.
Of course, by suitably shaping the pole gaps 44 (cf. e.g. the U.S.
application Ser. No. 570,873, FIG. 4), the sensor 46 could also be
arranged in the air gap 29, i.e., in the region of useful flux, in
which case a conventional Hall generator would suffice.
A flat motor according to the invention is, with respect to
economical manufacture, realizable even in mass production
particularly with the further disclosed modifications.
FIG. 8 depicts a section similar to FIG. 3, through a third
exemplary embodiment, but at true scale
FIG. 9 depicts the section according to line IX--IX of FIG. 8
FIG. 10 shows the section according to line X--X of FIG. 8.
The third exemplary embodiment depicted in FIGS. 8 to 10 offers in
this connection an advantageous alternative solution and is, in
other respects, to a great extent constructed the same as in the
relevant preceding Figures.
This can be seen from such a use of reference characters which is
the same as in FIGS. 1 to 7 or else is missing.
The different parts, however, are differently denoted.
The fan housing of FIGS. 8 and 9 has the dimensions: h=25 mm,
g.times.g=76 mm.times.76 mm. The plate 220 indicated in FIG. 9 as a
circumferential edge by means of the broken line 229 has (similarly
to what was described relative to FIG. 4) a printed circuit which
contains the entire electronics with the conductor connections
including the connections to the stator windings. Mainly, the power
components on it are located between the periphery of the fan wheel
and the discharge opening 16 in the region of the air flow. The
rotor-position detector is arranged as a "normal" Hall generator
246 (without IC) in the region of useful flux (greater induction
than in the stray field) of the motor, i.e., inward of the ring
magnet 230 on the plate.
FIG. 8 depicts in contrast to the embodiment of FIG. 3 a hat-like
molded piece 258 which not only favors the entrance of the flow
(arrow 300) due to a truncated-cone-shaped hub, but which as a
synthetic plastic molded part in one-piece fashion with the blades
263 forms the fan wheel and advantageously from the economic
standpoint holds encompassed the same flux-return rings 259 (as
denoted by 26 on the stator), on which the permanent ring 230 of
the rotor is magnetically and mechanically secured. Its structure
is formed, with almost complete motoric quality according to FIG.
10, by component magnets 231 to 234 which are trapezoidal and
identical to each other and which can be formed from strip material
in pairs without any waste of material using the simplest tools;
the trapezoidal form of these magnets is determined by two right
angles and one 45.degree. angle. The distances between neighboring
component magnets forms the pole gaps, here as in FIG. 5 inclined
in the rotation direction 243 proceeding from outward to inward.*
The hat-like molded piece 258 can also be made of a light-metal
pressure-molded part (made of Al or Mg alloy).
The hub is stiffened by radial planar ribs 256, while there is
injection molded in them a metal bushing 257 with an out-of-round
edge in which the shaft 37 is force-fitted. Alternatively, a shaft
with a locally (at the location 357) roughened surface is inserted
in the molded piece 258 non-rotatable relative thereto, e.g.,
cemented in.
In FIG. 5 the angle .eta. is indicated. It is the acute angle
(<90.degree. ) *between the straight line (33) through the coil
centers and the next-lying, considered opposite to the rotation
direction (43), normal (133) (perpendicular) on one end face
(indentation) of the reluctance iron (38) (or the next-lying,
considered opposite to the rotation direction 43, angle-bisecting
line (133) between two projections (38') and (38") on the
reluctance iron (38)).
The angle .eta. amounts optimally, with a rotor having p pole pairs
to
if the pole gaps (denoted by 44 in FIG. 5) are radially
oriented.
The optimal value for .eta. with inclination of the pole gaps from
radially outward toward radially inward in the rotation direction,
is .eta..sub.o to 2/3.times..eta..sub.o (with greater inclination
decreasing).
The optimal value for .eta. with inclination of the pole gaps from
outward toward inward counter to the rotation direction of the
rotor is .eta..sub.o to 4/3 .eta..sub.0 (with greater inclination
increasing).
Between the angles .epsilon. and .eta. there exists the general
relationship
* * * * *